Photodegradation mechanism on recalcitrant substrates in the TiO2 photocataritic degradation

河流、湖泊等地堆积着即使通过细菌修复也不能降解的化学物质。它们对水环境造成了严重的生态破坏。本研究重点研究了持久性有机污染物的解毒和净化过程。(1)采用二氧化钛光催化降解难降解的三嗪类农药，最终生成的三聚氰酸不会矿化为二氧化碳。三聚氰酸不能被二氧化钛降解。通过氧化锌对三聚氰酸的光诱导降解，阿特拉津农药中的三氮杂环很容易被二氧化碳和硝酸根离子氧化。在光催化降解氯代/氟代苯甲酸同系物方面，甲酸和醋酸在较短的光照时间内容易发生苯环开环反应，生成二氧化碳。邻位和对位的脱氯比间位的脱氯更容易发生。然而，所有同系物的脱氟都很困难。利用TOF-MS对含C-F基团的中间体氧化产物进行了鉴定。(3)全氟表面活性剂如PFCA和PFSA不能被二氧化钛矿化成含氟离子，但在均相催化剂聚钨酸盐的催化下可以低产率地脱氟，并详细揭示了光强、波长、催化剂负载量和pH值等最佳实验因素以及降解机理。

Chemical substances which can not be degraded even by bacteria remediation are accumulated in rivers, lakes and other. They cause a seriously ecological damage in aquatic environment. The detoxification and purification procedure for persistent organic pollutants were focused in this study.(1) Non-degradable triazine agrochemicals were photocatalytically decomposed with titanium dioxide, followed by the final production of cyanuric acid not to be mineralized to carbon dioxide. Cyanuric acid can not be degraded with titanium dioxide. The triazine ring in the atrazine agrochemicals can be easily to carbon dioxide and nitrate ion by the photoinduced degradation of cyanuric acid with zinc oxide. The triazine compounds can be photocatalytically degraded by using titanium dioxide together with ozone in a high yield.(2) Concerning the photodecomposition of chloro/fluoro benzoic acid homologs the benzene ring-opening occurred easily in a short illumination time to evolve carbon dioxide via formic acid and acetic acid. The dechlorination for the ortho-position and para-position happened more easily than that for the meta-position. However, the defluorination for all homologs was difficult. The intermediate oxidative products bearing C-F group were identified by TOF-MS spectroscopy.(3) Perfluoro surfactants such as PFCA and PFSA could not be mineralized to florinated ion with titanium dioxide, but the defluorination was possible with homogeneous catalyst of polytungstanate in a low yield.The optimum experimental factors such as light intensity, wavelength, catalyst-loading and pH value, as well as the degradation mechanism were revealed in detail.